Gravitomagnetism
Gravitomagnetism is the name given to the proposition that gravity, like electromagnetism, has a second field component produced not by mass but by mass in motion — so that a rotating body drags the space and the orbits around it in a way Newtonian gravity cannot describe.
The standard account
The idea predates general relativity. Oliver Heaviside proposed in 1893 that gravitation might be described by a pair of coupled field equations formally identical to Maxwell's, with a gravitational analogue of the magnetic field. In general relativity the same structure reappears as a limiting case: in the weak-field, slow-motion approximation the Einstein field equations linearise into a Maxwell-like form, with a gravitoelectric field reproducing Newtonian attraction and a gravitomagnetic field generated by mass currents.
Its best-known prediction is the Lense–Thirring effect (1918), or frame dragging: a gyroscope in orbit around a rotating mass precesses. The effect is tiny. Gravity Probe B, which flew from 2004 to 2005 with four cryogenic gyroscopes in polar orbit, reported a frame-dragging precession consistent with general relativity, though with a much larger uncertainty than the accompanying geodetic precession; satellite laser ranging to the LAGEOS and LARES satellites has been used to make the same measurement by a different route. Both determinations remain far less precise than most other tests of general relativity, and this is a real and acknowledged weakness rather than a manufactured one.
An important formal caution: in general relativity the Maxwell analogy is an approximation valid in a restricted regime, not an exact structural identity, and the sign conventions and factor-of-two differences from electromagnetism are frequently mishandled in the secondary literature.
On this wiki
Gravitomagnetism is one of the most heavily developed themes in this collection, chiefly through one researcher.
Thierry De Mees has built an entire programme on it, treating the second field — which he calls gyrotation — as a real Heaviside-style field rather than a metric approximation. His foundational papers are A Coherent Dual Vector Field Theory for Gravitation and Analytic Description of Cosmic Phenomena Using the Heaviside Field, with the results collected in Gravitomagnetism: Successes in Explaining the Cosmos and Gravitomagnetism - Gravity beyond Einstein - including an introduction to the Coriolis Gravity Theory. The claim that gives the programme its force is that a Newtonian-style dual-field theory reproduces, without curved spacetime, phenomena normally cited as evidence for general relativity or for exotic matter:
- flat galactic rotation curves without dark matter — Deduction of Orbital Velocities in Disk Galaxies. "Dark Matter": a myth?;
- the perihelion advance of Mercury, which he attributes to the Milky Way's own field — Mercury's Perihelion Advance is Caused by Our Milky Way;
- the bipolar symmetry of supernova remnants — The Observed Symmetrical Supernovae Remnants Form Overwhelming Evidence for the Gravitomagnetic Force (see Supernova);
- planetary spin, ring systems and the inflation of planetary bodies.
He also argues on historical grounds, in Did Einstein Cheat? How Einstein Solved the Maxwell Analogy Problem, that the Maxwell analogy was available and was passed over.
Oleg D Jefimenko reached a related position from classical electrodynamics, developing a causal, retardation-based gravitational theory containing a second "cogravitational" field — a line of work independent of general relativity and pursued in classical field terms.
The wiki does not present a single view. Jerry Hynecek argues the opposite case in Why there is no Gravitomagnetic Force, and this internal disagreement is worth taking seriously: the analogy's validity is disputed among the researchers catalogued here, not only between them and the mainstream.
On the experimental side, Martin Tajmar reported apparently anomalous gravitomagnetic-like signals around rotating superconductors — many orders of magnitude larger than general relativity allows — in Measurement of Gravitomagnetic and Acceleration Fields around Rotating Superconductors and Investigation of Frame-Dragging-Like Signals from Spinning Superconductors using Laser Gyroscopes. The related superconductor–gravity coupling claims of Ning Li and Douglas G Torr are catalogued here as well, and are the main bridge between this topic and antigravity research. None of these laboratory claims has been independently confirmed, and this should be stated as plainly as the claims themselves.